Filter bed cleaning device for sewage clarification tanks



y 3 1933- w. c. LAUGHLIN ET AL 1,919,567

FILTER BED CLEANING DEVICE FOR SEWAGE CLARIFICATION TANKS Filed Aug. 4,1951 5 Sheets-Sheet 1 v w I INVENTORS iVz/llmw /T Away/dim ,d/vz/ z zjgjiAlrr/z July 25; 1933- w. c. LAUGHLIN ET AL 1,919,567

.FILTER BED CLEANING DEVICE FOR SEWAGE CLARIFICATION TANKS Filed Aug. 4,1931 3 Sheets-Sheet 2 I INVEN Tom William [ffiaay/z/l/z 3 Aha/2am B.JZ/i;

IIIIIIIIIIIIIIIII/ 5% A T TORNEY y 1933- w. c. LAUGHLIN ET AL 1,919,567

FILTER BED CLEANING DEVICE FOR SEWAGE CLARIFICATION TANKS Filed Aug. 4,1931 3 Sheets-Sheet 3 4 321? ORNEY Patented July 25, 1933 UNITED STATES-relate? PATET; OFFICE WILLIAM C. LAUGHLIN, OF KEW GARDENS, AND AB i a: aA863, or ascents,

NEW YORK, ASSIGNOBS TO FILTRATION EQUIPMENT COPOEATION, O! NEW YORK,

N. Y A CORPORATION OF DELAWARE FILTER BED CLEANING DEVICE FOR SEWAGECLABIFIOATIOH TANKS Application filed August 4, 1981. Serial Io.555,054.

Our present invention relates to sewa e clarification tanks, moreparticularly to tan of the character which are furnished with filterbeds for filtering out impurities; and

, the invention has for its pur use and ob'ect to enmeshed in the filterbed, will be separated from the efiluent liquid. A further object is tocollect the separated dirty water, solids and impurities and to draw thesame out of the tank for re-circulation or for such other disposition asmay be desired, while permitting the clarified eflluent to rise toits'discharge outlet by reason of its natural movement towards itsliquid level.

"will be forced to the elevation necessary For the attainment of itsobjects,-the invention in its evolvement has in view the provision of awater-head for receiving ,the inflowing sewage liquid or material andthe level of this water-head is at an elevation above the dischargeoutlet for the clarified effluent. Over the filter bed is arranged atraveling filter bed cleaning device having a collector chamber; and thefilter bed and cleaning device are so relatively. positioned that theinlet to the collector chamber is below the level of the dischargeoutlet, so that by reason of the elevation of the water-head, the liquidin the immediate territory of the cleaning device will be forced overthe inlet into the collector chamber, whereas the liquid outside of theterritory of the cleaning device to pass through the discharge outlet.Accordmg to a feature of the arrangement, the inlet to the collectorchamber is restricted; and it is made adjustable as to height so. thatthe level of this inlet may be varied with respect to the level of thewater-head. By virtue of this rovision, the pressure and velocity of theliquid upwardly through the filter bed in the territory of the cleaningdevice may be controlled.

It is within the province of our invention v to furnish the clean'device with means whereby to agitate or stir up the sand or magnetitecomposing the filter bed so that the matter enmeshed therein will bepromptly released into the current which movessup aardly into the inletto the collector charm i The arrangement also includes the provision ofa discharge pump for pum ing the dirty water and impure substancescollector chamber as rapidly as they accumulate therein.

cm the Another object of the invention resides in a the provision of anoverhead carriage or trolley which carries the sand cleaner with itsmeans for agitating the filter bed and also the discharge pump, and thecarriage is equi ped with wheels which turn on ide trac rails positionedalong the top 0 the tank. The carriage may be nipped with a power unitwhereby to be sel -propelled on the track rails.

Bdy means of the carriage or trolley, the san cleaner is movedcontlnuously alorg the filter bed so that the sand or" magnetitecomposing the bed is not permitted to become sufiiciently dirty toobstruct filtration. The

cleaning operation ma be conducted con-v tinuous] along the be and maybe carried out by ydraulic means, or by mechanical means, or by magneticmeans, or by various combinations of these several agencies.

Other ob'ects and advantages of the invention wil appear hereinafter.

The invention resides in the new and novel features of construction andoperation and the new and original arrangements and com bination ofparts contained in the improved filter bed cleaning system hereinafterdescribed and more particularlyset forth in the claims.

Several simple and ractical embodiments of our invention are il ustratedin the accompanying drawings, in which throughout the several views likecharactersof reference indicate like parts, and in which Figure 1 is atop plan view of a sewage I only the opposite end portions of the tankappear in the view;

ig. 2 is a vertical cross sectional view through the tank, taken on theline 2-2 of Fig. 1, and showing the filter bed cleaning apparatus in endelevation with parts broken awa Fig. 3 represents a fragmentarylongitudinal sectional view through a cleanin device having anelectromagnet and throng a portion of a filter bed furnished withmagnetite as the filtering medium, this view being taken on the line 3-3of Fig. 4;

Fig. 4 represents a top plan view of the parts shown in Fig. 3; v

Fig. 5 is a view similar to Fig. 3, but showing a filter bed having sandas the filtering medium andshowing an alternative form of the cleanerdevice which is capable of cleaningwthe sand;

ig. 6 is a fragmentary longitudinal sectional view, showing a modifiedform of con'-" struction in which the said cleaning device is equippedwith pins for stirring up the sand; and

Fig. 7 represents still another fragmentary longitudinal sectional view,showing an embodiment in which the sand-stirring pins are made in theform of tubes by means of which to eject liquid into the sand bed forstirring up the sand.

Referring now in detail to the accompanying drawings, 10 denotes ingeneral an elongated sewage clarification tank, which is fractionallshown in Fig. 1 with its entire interme iate portion broken away so thatonly the opposite end portions of the elon ated tank are illustrated.This tank may be uilt from concrete or any material that may be suitableor approved for the purpose. The end 11 of the tank is provided with aninlet 12 for'the inflow of the sewage liquid. A suitable conduit 13conveys the sewa e liquid for passage through the inlet 12. T e oppositelongitudinal side walls 14, 14 of the tank are each provided with alaunder or trough 15 for carrying away the efiiuent, and these laundersor troughs empty into a main conduit 16 by which the eflluent isconveyed away for disposition in any manner desired. Suitable walkways17 for the use of workmen and attendants may be provided in the.launders 15.

Internally the clarification tank may in general be constructed andarranged to carry through clarification operations in accordance withthe principles more fully set forth in the application of William C.'Laughlin, one of the applicants herein, Serial No. 499,- 195, filedDecember 1, 1930, for a Method of conditioning sewage. The interior ofthe tank is divided into a central chamber 18 and side chambers 19 bybaflles 20 located in the upper portion of the tank and which ter-vminate at their lower ends intermediate the height of the tank so as toprovide in the bot tom portion of the tank an open chamber 21 with whichthe central chamber 18 and each" of the side chambers 19 cancommunicate. The upper portion of the chamber 18 is divided oil bydownwardly extending baflles 22 which converge as they extend downwardlyin order to provide a restricted feed opening 23. The inlet 12 isindirect communication with the chamber 24 b tween the baflles 22, andthe sewage fluid WhlCh fills the space 24 constitutes a water-head thelevel of which is elevated above the spaced outlets 25 for the dischargeof theefiluent into the launders 15. By reason of the water-head, asiphoning action is provided for moving the liquid upwardly through theside chambers 19 for discharge through the outlets 25. In passing, it isto be noted here that the central chamber 18 two side chambers 19, 19and waterhead chamber 24 extend lengthwise of the tank, with the centralchamber 18 and waterhead chamber 24 occupying positions between the sidechambers 19, 19.

The inflow of sewage fluid through the inlet 12 may consist of rawsewage fluid from which all trash and grit have been removed;

or it may consist of a mixture of such raw sewage fluid withwater-imbibed cellulose resulting from beatings of paper in the presenceof water. The mass descends from the water-head chamber through therestricted feed opening 23 into the chamber 18 and thence into thebottom chamber 21, while new supplies are fed into the water-head untilthe fluid mass fills the lower chamber in the tank and rises in the sidechambers at the outer sides of the bafile walls 20. During the massmovement, the sewage solids, whether colloidal or suspended, areenmeshed or entangled in the cellulose gel so as to form a slime-likestrata of cellulose and sewage solids. Through a coagulating medium,present in the mixture or added thereto, the colloid constituents of themass, both the sewage solids and the colloidally conditioned fibers orcellulose gel, give up their imbibedwaterr Thereupon the coagulatedcolloids including the solids of the sewage, having a higher specificgravity than the water, settle downwardly to the bottom of the tank,while the lighter water, solids and impurities rise in the side chamberstowards the discharge outlets 25. The bottom of the tank is providedwith sloping portions 26 which slope toward a central channel 27. Therelatively heavy matter or sludge settles onto these sloping portionsand gradually moves to the channel 27 from where it is drawn off by asludge pipe (not shown) or other suita le discharging medium.

In the upper portion of each of the side chambers 19 and below thedischarge outlets 25 is provided a filter bed designated generally bythe numeral 28. The water and impurities rising in the side chambers 19by the siphoning action encounter the filter beds where the filteringout of the impurities takes place, and the clear water efiluentresulting from the filtering action rises upwardly for its dischargethrough the outlets 25. The filter beds may consist'of a bed either ofsand or of magnetite ore supported upon a suitable screen 29.

The apparatus for cleaning the filter beds includes a traveling carriagewhich is designated in general by the numeral 30 and which may consistof any suitable framework capable of carrying the various parts whichmake up the complete operative apparatus for cleaning the beds. At itsopposite ends, the carriage is provided with a pair of wheels 31 whichturn on track rails 32 provided upon the longitudinal sides 14 andinwardly of the positions of the efiuent launders 15. These track railsprovide for the movement of the carriage for the full length of thefilter beds so that the filtering medium can be cleaned throughout thelength of the beds. The carriage is furnished with its own power means,and such means preferably consist of an electric motor 33 which ismounted upon the framework, and, in association with the motor, areduction gear box 34 whereby from the motor shaft 35, to operate thedriving shaft 36 at reduced speed. The driving shaft carries a gear 37which is in drivingengagement with a gear 38 mounted upon a shaft or soaxle 39. At each end of the carriage, one of the two track wheels ismounted on the shaft or axle 39. Two filter cleaiiin devices areprovided, one for each of the lter beds 28. These cleaning devices,indicated in general by the numeral 40, are suspended from the carriageby means of suitable I-beams 41. Inasmuch as the two cleaning devicesare duplicates, a detail description of one of them will sufiice for theother.

In Fig. 5, we illustrate in its sim lest form a cleaning device suitablefoncleanmg a filter bed composed of sand 42. The device includes acleaner or cleaning tank 43 of a size to fit, transversely of the bed,between the bafile 20 and side wall 14, the fit in this regard beingsuch that while the opposite sides of the cleaner come in closeadjacency to said 7 res ctive parts, yet they do not contact with saiparts so as to provide frictional resistance. The bottom 44 of thecleaner is in close.

proximity to the top surface of the sand bed. The length of the cleanerin the direction of the length of the sand bed, is such as will define adefinite territory or area of resistance for the agitation upwardly ofthe sand under the pressure and velocity of the liquid rising throughthe sand. In the present instance the dimension of the cleaner,lengthwise of the bed, is increased by the provision of an apron orstrip 45 which is in ali ment with the bottom 44. This cleaner, tweenthe bottom 44 and apron 45, and for the full dimension of the cleanerbetween the baflles I20 and side wall 14, is provided with a neck orinlet opening 46 in communication with a feed 47 formed by two bafles48. A suitable screen 49 may be provided for the feed 47 be- .tionsindicated in the present instance consisting in the provision ofsuitable vertically extending slots 53 through which are assed pins 54provided with win nuts 55. nder this construction, it will observed thatthe inlet 46 is located substantially midway the length of the cleaner,so that for the territory of resistance afiorded by the cleaner thedirty water and impurities will rise through the inlet 46, feed 47 andinto the space 50 whence they pass over the weir into the interiorchamber 52. In Fig. 5, the line 56 indicates approximately the distancebetween the spill over the weir and the level of the water-head; whilethe line 57 indicates approximately the distance between the spillthrough the discharge openings 25 and the level of the water-head.

It will be apparent that by reason of the elevation of the water-head,any adjustment of the weir vertically will influence the pressure andvelocity of the liquid upwardly through the filter bed for the territoryoccupied by the cleaner. The weir, therefore, may be adjusted in thatprecise position which will cause the sand between the screen 29 at thebottom of the bed and the bottom 44 and apron 45 at the top of the bed,to be churned and agitated by the pressure and velocity of the watermoving under siphoning action to the inlet 46. In this way, the dirtywater, solids and impurities enmeshed and entangled in the sand withinthe territory of the cleaner and its apron, will be released formovement with the stream into the interior chamber 52. Outside theterritory occupied by the cleaner and its apron, the water rising fromthe sand bed where the sand has not been agitated or churned underresistance, is clean and rises un 61 the siphoning action to thedischarge out ets 25. The cleaner, it will be observed, shuts out theclean water, so that only the dirty water carrying the impuritiesreleased through the agitation and churning of the sand under measure,will enter the chamber 52; The irty water is removed from the chamber 52bymeansof a centrifugal pum 58 operated by an electric motor 59 locateupon the top of the tank where it is above the level of the flow ofclean water through the discharge openings 25. The dirty water andimpurities pumped out by the pump ma be disposed of in any suitableman-- ner. In ig. 4, we show, for instance, a dis-, charge pipe line 60connected with the pumpand arran d to discharge the dirty water andimpurities into the water-head for recirculation through theclarification tank- The carriage or trollefy, carrying the two cleaningdevices, moves orwardly and backwardl along the elongated tank so as tointerval y clean all portions of the two sand beds from one end thereofto the other. The carriage is kept in continuous movement and the ob ectis to clean all se ents of the sand beds so frequently that there willbe no opportunity for the sand to become very dirty. The cleaner thebeds are kept, the cleaner the eflluent' will'be. Owing to the provisionof the water-head which induces a flow of the liquid into the dirtywater chamber of each of the cleaning tanks and as well through thehigher discharge outlets 25, and the fact that each cleaning tank shutsout the clear water eflluent while defining a territory of resistance oragitation wherein the dirty water and impurities within the sand bed arereleased for movement with the stream into the dirty water chamber,there results a constant sep. aration of the impurities from the bed sothat in practice the latter is practically free of solids andimpurities. By returning the se arated dirty water and impurities backto t e water-head, these are put into a recirculation for re-treatmentwithin the clarification tank.

In Figs. 3 and 4, the cleaning device is illustrated as provided with anelectroma et 61 for agitating or churning a" filter be includingmagnetite or magnetite ore 62 as the filtering medium. The cleaningdevice, in this instance, is constructed so as to provide an inlet 63 ofa size suflicient to contain the electromagnet which is of elongatedform ".(Fig. 4) so as to extend substantially the entire width of thecleaning tank. The inlet 63 is defined by the upwardly convergingbaflles 64 and 65 formed respectively between the a ron 45 and thebottom 44 of the cleaner 43. n the bafile 65 is provided an adjustableweir 66 which forms with the bafile 64 a feed opening 67 through whichthe dirty water and impurities pass into the chamber within the tank 43.The electromagnet is thus carried by the cleaning device so as to comeabove the magnetite filter bed. The magnetite within the territory ofthe bottom 44 and apron 45 is attracted by the magnet and thereforemoves toward the magnet when the latter is energized. When the magnet isde-energized, the magnetite drops back on the screen. The magnetite iscaused to jump up and fall back as often as the current is turned on andoff.

itself to vibrate. This will also aid in kee ing the screen clean.Attention is especial dy called to the fact that the weir 66 is so aJusted that the magnetite will constantly be kept on the verge of movingupwardly by reason of the pressure of the upwardly s1- phoned liquid.When the magnetite is thus buoyed up by the liquid pressure, littlepower on the part of the magnet is required in order to move themagnetite.

. In the form of construction exemplified in Fig. 6, the baflies 68 and69 are arranged in 1 a manner similar to the bafiles 64 and65 of theconstruction shown in Figs. 3 and 4. In this 'case, instead of providlngan electromagnet, we employ stirring pins 70 which are secured to thebaflie 68 and which extend I downwardly through the inlet 71 and intothe sand of the sand bed 72. Upon the movement of the cleaning devicealong the top of the sand bed, the pins serve as rakes for stirring upand agitating the sand to effect the release of the dirty water andimpuri ties which are thereupon carried up by the stream through thefeed opening 73 provided between the adjustable weir 74-and the baflle68. In the present instance, the pins 70 are stationary; but they may,if desired, be mounted or movement on eccentrics or on rocker arms sothat the pins will be given an up and down or even a sidewise movementas the trolley travels along the clarivfication tank.

As exemplified in Fig. 7, the stirring pins may consist of tubes as 75and they may be connected up as the terminal portions of branchdischarge lines 76 which branch ofi from the main line 77 through whichthe dirty water and impurities are returned by the pump to thewater-head. In this case, the pins are provided with outlet ducts 78within the sand bed so that the dirty water expelled from the dirtywater chamber by the ump can be utilized in churning up the sand in thesand bed. The pins, whether of the solid type shown in Fig. 6 or of thetubular typeshown in Fig. 7, are arranged in a row or rows transverselyof the cleaning device so that as the trolley progresses the sand bedwill be stirred up throughout its width. In conjunction with theelectromagnet shown in Figs. 3 and 4, stirring pins may be used ifdesired.

It is to be understood that, in practice, the several embodiments ofcleaning devices may be made for use in connection with circularclarification tanks, or square clarification tanks, as well as forelongated tanks of the type herein disclosed.

It will be obvious that the several forms of construction hereindisclosed are capable of embodiment in many difi'erent environments. Ithas been sought herein to illustrate only such embodiments as willsuflice to exhibit thecharacter of the invention.

From the foregoing description taken in connection with the accompanyingdrawings, it will be manifest that wev have disclosed extremely simpleand thoroughly satisfactory' forms of cleaning devices for clarificationtanks, which devices embody the features we have enumerated in thestatement of the invention and as well in the foregoing description; andwhile we have, in the present instance, shown and described thepreferred embodiments for carrying out our invention in practice, it isto be understood that the constructions exhibited are susceptible ofmodification in various particulars without departing from the spirit orscope of the invention or sacrificing any of its advantages.

We claim 1-- l. A device for cleaning filter beds including, incombination, a separating chamber into which the dirty liquid from thebed may pass, and means for agitating a portion of the bed to translatethe dirttherein into dirty liquid, said separating chamber comprising atank for receiving the dirty liquid and having an upwardly extendinginlet leading to its interior, and means for regulating the height atwhich the dirty liquid will pafisk from the inlet into the interior ofthe ta 2. A device for cleaning filter beds including, in combination, aseparating chamber into which the dirty liquid from the bed may pass,and means for agitating a portion of the bed to translate the dirttherein into dirty liquid, said separating chamber comprising a tank forreceiving the dirty liquid and having an upwardly extending inletleading to its interior means for regulating the height at which thedirty liquid will pass from the inlet into the interior of the tank, andmeans for supporting the tank for moveits? in juxtaposition to thesurface of the 3. In a sewage tank, a filter bed arranged between thewalls thereof and including loose material for filtering the sewageiquid, means for causing sewage liquid to rise under pressure from belowthe bed upwardly through the material to a level thereabove, a carriagetraveling upon the walls of the tank, a cleaning device dependin fromthe carriage and having below the liquid level above the bed a liquidretaining chamber, said device including in juxtaposition to the surfaceof the bed a horizontally disposed barrier element which defines againstthe upwardly rising liquid a resistance and m WhlCh the pressure of theresisted liquid will cause agitation and washing of the material, and apassage through the barrier element leading to the liquid retainingchamber to permit the liquid with the dirt which it gathers from thematerial to rise under pressure for discharge into said chamber.

4. In a sewage tank, a filter bed arranged between the walls thereof andincluding loose material for filtering the sewage liquid, a head forcausing pressural movement of the liquid from a point below the bedupwardly through the material and to a liquid level thereabove, acarriage traveling upon the walls of the tank, a cleaning devicedepending from the carriage and having below the liquid level above thematerial a liquid retaining chamber, said device including injuxtaposition to the surface of the bed a horizontally disposed barrierelement which de fines against the upwardly moving liquid a resistancearea in which the pressural movement of the resisted liquid will causeagitation and washing of the material, and an upward passage through thebarrier element in communication with the liquid retaining chamber at apoint above the bottom thereof and below the liquid level above thematerial to permit the liquid with the dirt which it gathers from thematerial to rise under pressure for discharge into saidchamber.

5. A cleaning device for a filter bed having loose filtering materialthrough'which liquid under pressure will move upwardly, said devicecomprising a tank positioned to define over the material a resistanceterritory wherein the pressure of the liquid will cause agitation andwashing of the material so that the liquid will take up dirt from thematerial, said tank having a liquid containing chamber and an inletthrough which the dirty liquid from the resistance territory will entersaid chamber, and a weir adjustably associated with the inlet forestablishing the level at which the dirty liquid will enter the chamber.

6. A cleaning device for a filter bed having loose filtering materialthrough which liquid supplied from a head will rise under pressuralmovement,- said device comprising a tank positioned to define over thematerial a resistance territory wherein the pressure of the liquid willcause agitation and washing of the material so that the liquid will takeup dirt from the material, said tank having a liquid containing chamberand an inlet through which the dirty liquid from the resistanceterritory will enter said chamber, said chamber and inlet being belowthe level of the-head, a weir adjustably associated with the inlet forestablishing the level at which the dirty liquid will enter the chamber,said weir being adjustable with respect to the level of the head forvarying through the material the pressural movement of liquid suppliedby the head.

7. Means for cleaning a filter bed composed of granular material andarranged to filter liquid which is forced under a pressure head to riseupwardly through the material and to a liquid level above the bed, saidmeans comprising a body constructed to provide resistance to thepressural tide of the liquid at the top of the bed, to establish byreason of the conflict between the pressural tide and resistance, anagitation of the material whereby to release dirt from the material,said body including a liquid-receiving chamber and an inlet to thechamber for the passage thereto of the dirty liquid which results fromthe agitation of the-material, the discharge point 'of the inlet intothe chamber being located at a level lower than the liquid level toinsure movement of the dirty liquid through the inlet and into thechamber under the force of the ressure head, the said discharge pointconsisting of a weir adjustable upwardly and downwardly with respect tothe liquid level for controlling movement of the tide destined to passto said chamber.

8. In a sewage system, the combination with a filter chamber having afilter bed and a pressural upflow of liquid through the material of thebed, of a barrier obstruction moving lengthwise of said chamber injuxtaposition to the surface of the material for resisting the pressuralupflow of liquid, a dirty water receiving vessel mounted upon thebarrier obstruction, an upwardly extending passage through which thepressural upflow will rise to said vessel, said passage being in opencommunication with the surface of the material and consisting of bafllewalls which rise higher than the bottom of the vessel.-

9. In a sewage s stem comprising, with a filter chamber, a ter screendividing the chamber into lower and .upper sections, a bed of loosefiltering material disposed upon the screen, said upper section havingan efiluent outlet at a evel above the material, means for maintaining aressural flow of sewage liquid from the ower section up through thescreen and material and to the level of the efiluent outlet in the uppersection, a carriage traveling lengthwise of the upper section, a devicemovable by the carriage for cleaning the material, including a barrierin juxtaposition to the surface of the material for resisting pressuralupflow of the liquid in a zone transversely of the bed, said barrierbeing efiective to cause the resisted liquid to agitate and wash thematerial, a vessel comblned with the barrier for receiving dirtygiiquid,an upwardly extending passage conducting under pressural upflow thedirty liquid from the washing operation to said vessel, said passagehaving within the limits of the barrier open communication with thematerial and extendin in a zone transversely of the bed, with t edelivery end of the passage in a plane below the efiiuent liquid level.

'10. In a clarification system including a bed of sand or the like forfiltering moving liquid, a tank adapted to be moved parallel to the bedand having a horizontally disposed bafile wall in juxtaposition to thesurface of the bed, an inlet within the outline of the bafiie wall, opento the bed to capture liquid of the bed and discharging into theinterior of the tank at a point above the bottom thereof, said bafiiewell being effective to resist movement of the liquid from the bed andcausing agitation of the liquid and hence of the sand below such wall,and said inlet affording a passage through which the'liquid of igitationmay rise for discharge into the tan 11. A sewage clarification system,comprising a-filter bed arranged between side walls forming a channelabove the bed, a carriage traveling upon the side walls and carrying atank within the channel parallel to the bed, said tank being open to theatmosphere, bafile means disposed in juxtaposition to thesurface of thebed and extending substantially the whole distance between the sidewalls to produce within the bed a backwash area for agitating andwashing the bed from side wall to side wall as the tank moves along thebed, an inlet permitting dirty liquid from the backwash area to passdirectly into the interior of the tank at a point above the bottomthereof, and a pump and pump line for drawing off the liquid whichenters the tank, said pump being (118 within the tank and said inletbeing so disposed as not to permit efiective action of the pump upon theliquid on its way to the tank.

12. In a sewage system, the combination with a filter chamber having afilter bed and a pressural upflow of liquid through the material of thebed, of a barrier obstruction moving lengthwise of said chamber injuxtaposi-' tion to the surface of the material for resisting thepressural upflow of liquid, a dirty water receiving vessel mounted uponthe barrier obstruction, an upwardly extending passage through which thepressural upflow will rise to said vessel, said passage being in opencommunication with the surface of the material and consisting of bafilewalls which rise higher than the bottom of the vessel, and a screen onthe bafliewalls extending across said passage for eliminating anymaterial of the bed borne by the upflow.

' WILLIAM C. LAUGHLIN. ABRAHAM B. ASCH.

